The main body of a conventional rubber crawler is formed of vulcanized rubber chiefly consisting of natural rubber. As shown in FIGS. 5A and 5B, metal core bars 2' are embedded in the circumferential direction of the rubber crawler body 1' at a fixed interval; a number of steel cords 3' are aligned and embedded on the ground side of the core bar 2' (steel cords 3' are split on both sides of engageable holes H for a driving sprocket and embedded to comprise a layer under wing portions 2'b of the core bars 2'); and ground face lugs P formed of the vulcanized rubber are provided on the ground side of the rubber crawler body 1'.
To compare with a steel crawler, this rubber crawler has many advantages, especially in not damaging a paved road surface, and therefore has been in wide use.
However, it still has problems such as producing mechanical noise and vibrations due to lack of support for rolling wheels at the intervals between core bars, as well as having great weight because a great number of core bars, steel cords etc. are to be embedded in the crawler body to resist the great driving force from a driving sprocket. Besides, the driving sprocket may fall off the crawler due to the lack of the rigidity of the crawler body between the embedded core bars.
On the other hand, a rubber crawler wherein the whole body is composed of highly elastic and rigid urethane rubber seems to solve the above problems.
However, it also has the following problems:
(a) It causes trouble in rolling and meshing with a driving sprocket because the high elasticity of the crawler makes the whole crawler body hard to bend. PA1 (b) Though urethane rubber has a good durability against compression and distortion, its durability against extension is poor, and therefore cracking and cut flows grow rapidly in the continuously stretched parts. As a result, reinforcing members in the crawler body are exposed to the outside and to damage. PA1 (c) Urethane rubber has a problem with abrading concrete road surfaces. (In this regard, urethane rubber is not always superior to vulcanized rubber, such as natural rubber, etc.) PA1 (d) Urethane rubber is expensive.
The purpose of the present invention, therefore, is to solve the above problems with a highly elastic rubber crawler having no core bars. That is, no conventional core bars having projections are embedded.